The present invention relates to a scanning probe microscope.
FIG. 10 is an outline view of an atomic force microscope (AFM), which is one type of scanning probe microscope (SPM) of the related art. In FIG. 10, reference numeral 1001 is an XYZ translator, 1002 is a sample stage, 1003 is a sample, 1004 is a cantilever, 1005 is a cantilever deflection detector, 1006 is a controller, and 1007 is a computer.
In this related art AFM, the sample 1003 is mounted on the sample stage 1002 above the XYZ translator 1001, the sample 1003 is brought into contact with a sharpened probe fixed to the tip of the cantilever 1004, and the sample is scanned in the X-Y plane by the XYZ translator 1001. During this time, deflection of the cantilever is monitored by the deflection detector 1005, the controller 1006 performs feedback control so that deflection is fixed, and the position of the sample 1003 in the Z direction is adjusted by the XYZ translator 1001. Microscopic structures on the sample surface can be observed by mapping adjustment amounts for each position on the surface of the sample onto a screen using a computer.
As has been described for the related art technique, with an SPM the probe performs a raster scan relative to the sample using the XYZ translators. A piezoelectric body is used in many XYZ translators. A piezoelectric body can perform high resolution scanning with extremely small amounts of displacement per unit of applied voltage. On the other hand, however, because a voltage displacement curve of the piezoelectric body exhibits hysteresis, and is not linear, and because creep and drift arise, the shape of a scanning region is distorted and measurement accuracy is reduced.
FIG. 11 shows operation of the related art SPM, with reference numeral 1101 being an intended observation region, and 1102 being an actually observed region. Reference numerals 1103 and 1104 respectively represent a high scanning frequency axis and a low scanning frequency axis of the raster scanning. Putting it simply, in the case where an appropriate voltage is applied to a region 1101 obtained from a displacement amount per unit of voltage and scanned, the actually scanned region is distorted as shown by 1102 due to initial hysteresis etc., and reduced accuracy is caused because an observation image is generated with this as the region 1101.
With current SPMs, it is common to use a linear rise method where amounts of hysteresis and creep etc. are measured beforehand, a time voltage Curve is obtained so that amount of displacement of the XYZ translator becomes linear with respect to time, and a voltage based on this curve is applied to remove the effects of hysteresis etc.
Also, methods are being considered where amount of displacement of the XYZ translator is measured using a displacement sensor, and an image is generated based on this amount of displacement. Methods are also being considered where amount of displacement of the XYZ translator is measured using a displacement sensor, and scanning is performed while carrying out feedback control based on this amount of displacement.
However, with the linear rise method, there is the disadvantage that operation also varies with deterioration with age of the XYZ translator and changes in scanning frequency, and accuracy is reduced. Also, with the method of generating an image based on displacement sensor values, there is the drawback that the amount of data and computation required to generate the image is enormous. With the method of carrying out feedback control, there is the problem that scanning frequency is limited by the processing speed of the control system.
The object of the present invention is to solve the above described problems in a scanning probe microscope, and aims to provide a high precision scanning probe microscope that is not subject to the influence of hysteresis of a piezoelectric element or deterioration with age, reduces the amount of data and computation required to generate an image, and is capable of expanding the scanning frequency band limits.
In order to achieve the above described object, a scanning probe microscope of the present invention comprises scanning control means for controlling raster scanning of an XYZ translator, and displacement detection means for detecting amount of displacement of the XYZ translator, and is configured so that of the two raster scanning axes, only displacement of the XYZ translator along a low frequency scanning axis is feedback controlled, displacement of the XYZ translator along a high frequency scanning axis is made larger than a region to be observed, and an amount of displacement of the XYZ translator is sampled at the same time as a relative position of a probe enters into the observation region.
With this configuration, the effects of hysteresis or deterioration of the translator with age are removed, the amount of data and computation at the time of image generation is reduced, it is possible to make the scanning frequency high without raising the bandwidth of the control system, and it is possible to provide a high precision observation image with no distortion.